b-Quark physics as a precision laboratory: a collection of articles on the present status and future prospects

The quest for a few fundamental 'building blocks' of matter is one of the oldest and far-reaching queries of mankind.But it took two thousand years to turn a largely philosophical concept into a real scientific question.Combined developments in chemistry, mathematics and physics paved the road to a qualitative understanding of the innermost structures of the world around us.They culminated in the discovery of quantum physics which opened the door to atomic scales, into the innermost structures of matter.With ever evolving experimental and theoretical possibilities, the quest for the smallest constituents of matter revealed that, besides the three known 'particles' proton, neutron and electron, there are many more.Further on, it was realized that proton and neutron as well as the other particles are themselves composed of two or three quarks, and there are three different quarks, up, down and strange.Some of these are unstable, and therefore not necessary as building blocks, but are required to explain many experimental and theoretical findings, including the fundamental fact that the universe and our world as we see them exist.It turned out that these new particles are grouped into 'generations', repeating the structure of the stable constituents of matter, the up and down quarks, the electron and the neutrino.Thus, these were discovered the strange quark, the muon and its neutrino, and, in 1974, the charm quark.In that year, the second generation was completed, confirming theoretical expectations and the basic structure of the quarks and leptons.In the subsequent years, the third generation, consisting of the tau and its neutrino, the b-quark, (bottom quark, 1976) and the top quark were discovered; but no further layer has been found until today, making the study of the third (and possibly last?) generation particles especially interesting.As pointed out, the existence of more than one and two generations is intimately related to several fundamental facts.Therefore, the study of these particles and their processes, often called flavor physics, is essential for our understanding of the laws underlying our world, formulated in a theoretical framework known as the Standard Model of particle physics (SM).In these efforts, the b-quark plays a central role and many important insights have resulted from these studies.The B -hadron system, that is all particles containing a b-quark is attractive and interesting for a variety of reasons.For one, its mass of ∼ 5 GeV is larger than the energy scales ∼ 1 GeV below which Quantum Chromodynamics (QCD), the theory of strong interactions, is non-perturbative.It is thus sufficiently heavy to give rise to a new effective theory of the SM, associated with heavy quark expansion, and to allow a perturbative treatment of QCD, using renormalization group techniques and diagrammatic calculations.This makes it a reliable laboratory for comparing experiment and theory, including lattice calculations.On the other hand, it is light enough to be produced in copious quantities at present experimental facilities.The b-quark lives sufficiently long to hadronise and to produce a large number of long lived exclusive final states when it decays.This allows to probe its properties in many complementing ways, giving a full picture of its properties.Since it decays also and predominantly into charm quarks, it is also a rich source of charm quarks.B -physics has developed considerably over the last thirty years, and there has been a lot of progress, also on issues that looked forbidding 20 or 30 years ago.We can say today that the accuracy and consistency of results reached today are a solid basis for further dedicated work.Thus, it is a good moment to take stock of these